This invention relates to a cylinder apparatus driven by pneumatic pressure, as well as to a method of controlling the cylinder apparatus.
In the prior art, speed control of a pneumatic cylinder apparatus is carried out by an arrangement of the kind shown in FIG. 1. The construction of this conventional pneumatic cylinder apparatus will be described with reference to FIG. 1.
As shown in FIG. 1, an air supply source 122 is a source for supplying compressed air to a pneumatic rodless cylinder 102. Connected to the air supply source 122 is a filter 120 for removing impurities such as oil from the air supplied by the air supply source 122. A pressure regulator 118 is connected to the filter 120. Accordingly, after the air supplied by the air supply source 122 has any impurities removed via the filter 120, the air is elevated to a predetermined pressure by the pressure regulator 118. The air thus elevated in pressure by the pressure regulator 118 is supplied to a 2-position 3-port solenoid valve 112 whence the air is supplied to the pneumatic rodless cylinder 102 via a speed control valve 106 or 108.
A solenoid 110 is connected to the solenoid valve 112. By turning the solenoid 110 on and off as necessary, the position of the solenoid valve 112 is changed over to switch between a state in which the compressed air from the pressure regulator 118 is supplied to a first air chamber 102a of the pneumatic rodless cylinder 102 and a state in which the compressed air is supplied to a second air chamber 102b of the pneumatic rodless cylinder 102. A muffler 114 and a muffler 116 are connected to respective ones of two ports of the solenoid valve 112. Air discharged from one air chamber of the pneumatic rodless cylinder 102 is released into the atmosphere.
The movement and operation of a piston 104 in the conventional pneumatic cylinder apparatus thus constructed will now be described.
Operation for moving the piston 104 from the left side to the right side in FIG. 1 will be described. First, the solenoid 110 connected to the solenoid valve 112 is placed in the OFF state to place the solenoid valve 112 in the position shown in FIG. 1. In this state, the air from the air supply source 122 is fed into the pressure regulator 118 and air at a predetermined pressure is discharged from the pressure regulator 118. The compressed air discharged from the pressure regulator 118 is supplied to the speed control valve 108 upon passing successively through a second port 112a2 and a fourth port 112a4 of the first chamber of 112a of solenoid valve 112. The air that has passed through the speed control valve 108 is supplied to the first air chamber 102a of the pneumatic rodless cylinder 102. As a result, pressure for moving the piston 104 to the right is produced in the first air chamber 102a.
Meanwhile, the air in the second air chamber 102b of the pneumatic rodless cylinder 102 is charged from the muffler 114 upon passing successively through the speed control valve 106 and a fifth port 112a5 and third port 112a3 of the solenoid valve 112. When the air is charged from the interior of the second air chamber 102b, the flow rate of the air discharged is regulated by the speed control valve 106 so that the traveling speed of the piston 104 is controlled so as to be rendered constant.
If the position of the solenoid valve 112 is changed over by the solenoid 110 when the piston 104 is moved from the right to the left side, compressed air is fed into the second air chamber 102b of the pneumatic rodless cylinder 102 and the air within the first air chamber 102a is discharged into the atmosphere. The position 104 is moved from the right to the left side.
However, a problem is encountered in the example of the prior art mentioned above. Specifically, consider the operation for moving the piston 104 from the left side to the right side, by way of example. Since the speed at which the air is discharged from the second air chamber 102b, namely the air chamber on the side at which discharge takes place, is limited by the speed control valve 106, the piston 104 is acted upon by a reaction force produced by the pressure within the second air chamber 102b. Consequently, acceleration of the piston 104 at starting time declines and, hence, movement of the piston takes time.
As an expedient for solving this problem, a method has been considered in which, by way of example, the air chamber on the discharge side is connected directly to the muffler without providing the speed control valve, thereby making it easier for the air to be discharged. In the case of this arrangement, the piston can no longer be controlled so as to move at a constant speed, but the arrangement is effective in a case where movement of the piston at very high speed is required more than movement of the piston at a constant speed.
However, in a case where the speed control valve is not connected to the air chamber on the discharge side, as described above, the piston 104 travels at high speed and back pressure that applies braking to movement of the piston 103 vanishes. This makes it necessary to provide a device such as a shock absorber, rather than a speed control valve, for the purpose of braking the piston 104. In is well known to employ a shock absorber that utilizes the elastic force of a spring for this purpose. If a strong spring force is used, however, the piston undergoes sudden deceleration and a large impact force acts upon the object being moved by the pneumatic cylinder. In the case of a weak spring force, the piston is not decelerated completely and strikes the wall surface of the cylinder, as a result of which the object being moved is still subjected to an impact force.
Since the optimum value of the above-mentioned spring force differs depending upon the weight of the object moved, it is required that the spring force be adjusted in dependence upon the type of object moved. The problem that arises is that this adjustment requires labor.
In a case where the object moved is of great weight, a very large shock absorber becomes necessary in order to absorb the kinetic energy of the object. In addition, the size of the pneumatic cylinder is enlarged owing to the space needed to install this shock absorber.